The traditional method for extraction of saccharide antigens characteristic of Group A Streptococci (GAS) involves the use of all liquid reagents. See e.g. Manual of Clinical Microbiology, 4th ed. (1985), page 171. This method is well known and can be used for diagnosis of streptococcal infection when performed in conjunction with an immunoassay. Typically, the extraction involves three liquid reagents: an acid (usually acetic acid, hydrochloric acid or citric acid), sodium nitrite and a neutralizing base or buffer (Tris, sodium hydroxide, etc.). These reagents are matched in terms of pH and molarity to produce optimal release of GAS saccharide antigen. A typical extraction involves the use of 150 .mu.l of 2M sodium nitrite, 150 .mu.l of 2M acetic acid and 350 .mu.l of 0.44M Tris/0.66N sodium hydroxide. The first two reagents (sodium nitrite and acetic acid) are mixed together in a tube and a swab containing the sample is placed into the solution. The reaction is incubated for 1 to 3 minutes and the third (neutralizing) solution is added and mixed. The swab is removed, a tip is inserted into the tube and the contents of the tube squeezed out onto a test device.
The procedure described above requires that accurate volumes of the three reagents be dispensed since the pH of the final solution must be approximately 7-8 in order to allow for the capture and detection of the released antigens in an immunodiagnostic assay.